JPS5848015B2 - Method for manufacturing enameled steel plate by continuous annealing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a steel plate for enameled steel having good enameled adhesion, nail skipping resistance, and press formability by continuous annealing.

The properties required of steel plates for enamel are that they do not cause nail skipping, which is a surface defect of the enamel caused by hydrogen gas;
These include no bubbles caused by carbon-based gas, good glaze adhesion, and little firing distortion.

Further, since enamel products are often subjected to severe forming and then enameled, deep drawability and other press formability are also required.

Enamel adhesion is obtained by applying an enamel glaze to a steel plate and then creating intertwined unevenness between the glaze and the steel base during the firing process, but many theories have been proposed regarding the detailed mechanism. It can be said that there is no theory that can explain all the phenomena that exist.

On the other hand, enamel products may be subjected to shocks during use, so if good adhesion cannot be obtained during enameling work, the glaze may peel off due to the impact, which will not only affect the beauty of the product but also affect the characteristics of the enamel product. Corrosion resistance, which is one of them, will also be impaired.

To solve this problem, conventional methods of enameling work include increasing the pickling weight by increasing the sulfuric acid pickling time as a pretreatment of the enamel, and adding elements such as P to the steel that improve the pickling speed. The necessary adhesion has been achieved through measures such as adding .

However, these measures cause disadvantages to enamel consumers, such as a decrease in productivity in the enamel work and an increase in processing costs due to an increase in pickling residue.

In view of the above circumstances, the present inventors investigated various methods for improving the adhesion of the steel plate by applying the steel plate twice during the production of steel plates for enamel by continuous annealing. It has been found that it is extremely effective to add 0.04% to 0.07%.

It is said that Cu, a trace element in conventional steel, significantly reduces the pickling speed of steel plates, and it is generally said that the adhesion of steel plates for enamels improves as the pickling loss value of the steel plate increases. .

From this point of view, Cu was considered to be harmful to adhesion.

However, as a result of various studies on the influence of trace elements in steel on adhesion, the present inventors found that the influence of the amount of Cu in steel on adhesion varies depending on the annealing method, as shown in Figure 1. It was found that box annealing and rapid heating, rapid cooling, and short-time holding type continuous annealing showed opposite trends.

In other words, when evaluating the adhesion after performing pickling treatment for a certain period of time, in the case of box annealing, the adhesion decreases as the amount of Cu increases, whereas in the case of continuous annealing, the adhesion decreases as the amount of Cu increases. It can be seen that there is a region where the amount of Cu is significantly improved.

The present invention is based on the above findings.

The present invention will be explained in detail below.

When producing the starting steel of the present invention, the amount of Mn is 0.40%
Steel shall be tapped as shown below.

The lower the Mn content (preferably 0.25% or less), the smaller the firing strain during enamel firing and the better the deep drawability, so the upper limit is set to 0.40%.

Next, Ti, S, and Cu are added to the molten steel in the ladle, during ingot making, or during continuous casting.
I is 0.01-0.30% (preferably 0.03-0.
10%), S is o. ois ~ 0.040% (preferably 0.020-0.030%) and Cu 0.0%
It is added in an amount of 4 to 0.07% (preferably 0.05 to 0.06%).

The reason why the Ti content in the steel sheet is limited to 0.01 to 0.30% (preferably 0.03 to 0.10%) is that the Ti content is 0.
．． If it exceeds 30%, the steel will harden and the manufacturing cost will increase, which is undesirable, and if it is less than 0.01%, no improvement in nail-skipping resistance or deep drawability can be expected.

The reason for limiting the S content in steel sheets is that the S content is o. oi
This is because if the content is less than s%, no significant effect of improving the nail chipping resistance can be expected, and if it exceeds 0.040%, there is a risk of red-hot brittleness.

In the present invention, Ti and S may be added to the entire steel ingot or slab, or to the core thereof.

Furthermore, when particularly excellent nail-skipping resistance is required, rare earth elements or Zr may be added to the steel together with S.

If Cu is less than 0.04%, good adhesion cannot be obtained by continuous annealing.

Moreover, if it exceeds 0.07%, it is not practical because the pretreatment pickling time required to obtain good adhesion becomes extremely long.

Cu may be added in the ladle, during ingot formation, or during continuous casting, but it is necessary to add Cu to the entire steel plate including its surface layer.

Slabs produced according to the present invention are hot rolled, pickled, cold rolled, electrically cleaned and continuously annealed if necessary, and temper rolled if necessary.

Hot rolling may be carried out under normally used conditions, but in order to prevent Cu from segregating on the surface layer of the hot rolled steel sheet, it is preferable to keep the rolling temperature as low as possible, and from this point of view it is 600°C or less. This is desirable.

The cold rolling rate is 30% to obtain the desired nail skipping resistance.
It is necessary that the ratio be 90% or less.

In other words, the appropriate cold rolling rate is 30% or more in order to obtain the necessary volume of voids to ensure nail-skipping resistance, and the generated voids are compressed and reduced. In order to prevent this, the appropriate range is 90% or less.

By carrying out continuous annealing according to the present invention, a steel plate for enamel can be obtained which has excellent nail-skipping resistance because the voids generated by cold rolling are well preserved.

The annealing temperature is 650°C or higher and 900°C or lower, preferably 70°C.
The temperature is 0°C or higher and 880°C or lower.

If the annealing temperature is below the lower limit, the softening of the steel due to recrystallization annealing is insufficient and desirable workability cannot be obtained.

Moreover, if the upper limit is exceeded, Cu tends to diffuse and segregate into the surface layer of the plate during annealing, making it impossible to obtain stable adhesion, which is not preferable.

If the annealing time is less than 20 seconds, recrystallization will not be completed and desired workability will not be obtained.

Moreover, if it exceeds 10 minutes, it is inappropriate for the same reason as the upper limit of the annealing temperature.

The present invention will be described below with reference to Examples.

Example 1 FeS and Cu were added to converter molten steel in a ladle, and the molten steel was subjected to vacuum degassing treatment to reduce the carbon content to 0.004 to 0.00. o
os%, and when making an ingot, pour the molten steel into a mold and leave it for 40 seconds to generate an initial solidification layer on the surface layer of the steel ingot, and add Hueguchi titanium to the core to form a steel ingot,
Blooming, hot rolling, plate thickness 3.5 mm, 520℃~6
Rolled at 00℃, pickled, rolled down to 1.0mm at 71%
Cold rolled at
% temper rolling was performed.

Table 2 shows the chemical composition of the kaihin board. In order to investigate the enamel adhesion of the finished board, it was heated in a 10% sulfuric acid solution at 70°C
After carrying out a pickling treatment for 20 minutes, the pieces were enamel-fired twice and the degree of peeling of the glaze was determined using an Erichsen tester.

The resulting rice is shown in Table 3.

As can be seen, the steel of the present invention has excellent adhesion.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing that the influence of the Cu content in steel on the adhesion of a pot plate for enamel differs depending on the annealing method. (Pickled in 10% H2SO4 at 70℃ for 4-5 minutes, burned twice, and judged adhesion using an Erichsen tester)
.

Claims (1)

[Claims] 1. Molten steel is tapped with a Mn content of 0.40% or less, and then subjected to vacuum degassing treatment, so that the Ti in the steel plate is 0.
．． After adding so that S is 0.01 to 0.30%, S is 0.018 to 0.040%, and Cu is 0.04 to 0.07% to form a steel billet or slab, hot rolling, Acid wash 3
Cold rolling at a rolling rate of 0% or more and 90% or less, then 65%
A method for producing a steel plate for enamel, comprising continuous annealing while holding the temperature in a temperature range of 0° C. or more and 900° C. or less for 20 seconds or more and 10 minutes or less.